The hydroformylation reaction, also known as the oxo reaction, is used extensively in commercial processes for the preparation of aldehydes by the reaction of one mole of an olefin with one mole each of hydrogen and carbon monoxide. The most extensive use of the reaction is in the preparation of normal- and iso-butyraldehyde from propylene. The ratio of the amount of the normal aldehyde product to the amount of the iso aldehyde product typically is referred to as the normal to iso (N:I) or the normal to branched (N:B) ratio. In the case of propylene, the normal- and iso-butyraldehydes obtained from propylene are in turn converted into many commercially-valuable chemical products such as, for example, n-butanol, 2-ethyl-hexanol, n-butyric acid, iso-butanol, neo-pentyl glycol, 2,2,4-trimethyl-1,3-pentanediol, the mono-isobutyrate and di-isobutyrate esters of 2,2,4-trimethyl-1,3-pentanediol. The hydroformylation of higher α-olefins such as 1-octene, 1-hexene and 1-tetradecene yield aldehyde products which are useful feedstocks for the preparation of detergent alcohols and plasticizer alcohols.
A low pressure hydro-formylation process using trialkylphosphines in combination with rhodium catalysts for the preparation of aldehydes has been described. Moreover, trialkylphosphines have seen much use in industrial hydroformylation processes but they typically produce a limited range of products and, furthermore, frequently are very oxygen sensitive. Other methods involve a low pressure hydroformylation process which utilizes triarylphosphine or triarylphosphite ligands in combination with rhodium catalysts. Such ligands, although used in many commercial applications, have limitations due to oxidative and hydrolytic stability problems. Since these early processes, numerous improvements have been made to increase the catalyst stability, catalyst activity and the product ratio with a heavy emphasis on yielding linear aldehyde product. A wide variety of monodentate phosphite and phosphine ligands, bidentate ligands such as bisphosphites and bisphosphines as well as tridentate and polydentate ligands have been prepared and disclosed in the literature.
Once such improvement involved a ligand design which employed halogen substituents on the phosphorus atom of trivalent phosphorus ligands. These halogenated phosphorus ligands are readily prepared and possess high activity, good stability and permit a wide N/I range of products to be prepared by simple variations in the process parameters.
Notwithstanding the substantial progress which has been made in the area of hydroformylation catalyst systems and catalysis in general, there still exists a need to develop more stable, less expensive and more selective catalysts systems with an emphasis on hydroformylation catalysts.